This thesis examines the skill of avoiding collisions with approaching moving objects, and in particular the competences of primary-school children and children with motor impairment. Pedestrian road crossing is chosen as the point of departure. Chapter 2 reviews children’s capacities on four component skills; namely, finding a safe place to cross, looking behaviour, perceptual judgements whether or not to cross, and the visual guidance of walking across the road. Chapter 3 and 4 aim to investigate whether the increased collision proneness of young children is associated with age-related differences in the perception of the affordance crossability and the visual control of movements. Chapter 5 and 6 aim to investigate whether the perception of the affordance crossability in children with hemiparesis is different from that in typically-developing children, and to identify the underlying movement planning and control processes that are involved in road- crossing behaviour of children with hemiparetic CP.Savelsbergh, G.J.P. [Promotor]Kamp, G.J. van der [Copromotor